EFFECT OF DIETARY ARACHIDONIC-ACID ON METABOLISM OF DEUTERATED LINOLEIC-ACID BY ADULT MALE-SUBJECTS

The influence of dietary supplementation with 20:4n-6 on uptake and tu rnover of deuterium-labeled linoleic acid (18:2n-6[d(2)]) in human pla sma lipids and the synthesis of desaturated and elongated n-6 fatty ac ids from 18:2n-6[d(2)] were investigated in six adult male subjects. T he subjects were fed either a high-arachidonic acid (HIAA) diet contai ning 1.7 g/d or a low-AA (LOAA) diet containing 0.21 g/d of AA for 50 d. Each subject was then dosed with about 3.5 g of 18:2n-6[d(2)] as th e triglyceride (TG) at 8:00 A.M., 12:00, and 5:00 P.M. The total 18:2n -6[d(2)] fed to each subject was about 10.4 g and is approximately equ al to one-half of the daily intake of 18:2n-6 in a typical U.S. male d iet. Nine blood samples were drawn over a 96-h period. Methyl esters o f plasma total lipid (TL), TC, phospholipid, and cholesterol ester wer e analyzed by gas chromatography-mass spectroscopy. Dietary 20:4n-6 su pplementation did not affect uptake of 18:2n-6[d(2)] in plasma lipid c lasses over the 4-d study period nor the estimated half-life of 24-36 h for 18:2n-6[d(2)]. The percentages of major deuterium-labeled desatu ration and elongation products in plasma TL, as a percentage of total deuterated fatty acids, were 1.35 and 1.34% 18:3n-6[d(2)]; 0.53 and 0. 50% 20:2n-6[d(2)]; 1.80 and 0.92% 20:3n-6[d(2)] and 3.13 and 1.51% 20: 4n-6[d(2)] for the LOAA and HIAA diet groups, respectively. Trace amou nts (<0.1%) of the 22:4n-6[d(2)] and 22:5n-6[d(2)] metabolites were pr esent. Plasma TL concentration data for both 20:3n-6[d(2)] and 20:4n-6 [d(2)] were 48% lower (P < 0.05) in samples from the HIAA diet group t han in samples from the LOAA diet group. For a normal adult male consu ming a typical U.S. diet, the estimated accumulation in plasma TL of 2 0:4n-6 synthesized from 20 g/d (68 mmole) of 18:2n-6 is 677 mg/d (2.13 mmole). Dietary supplementation with 1.5 g/d of 20:4n-6 reduced accum ulation of 20:4n-6 synthesized from 20 g/d of 18:2n-6 to about 326 mg/ d (1.03 mmole).